Hydraulic fluid composition



Patented Mar. 11, 1952 HYDRAULIC FLUID COMPOSIT ION Vito EspositofladdonHeights, N. J., assignor to R. M. Hollingshead Corporation,Camden, N. L, a corporation of New Jersey No Drawing; ApplicationOctober 17, 1949, Serial :No. 121,899

- 1 l The present invention relates generally to hydraulicfiuids usefulfor transmitting pressure in closed; systems and it relates moreparticularly to-a new and useful hydraulic fluid composition containingalkyleneoxide-treated tall oil.

Gonsiderable work has been done on the problem of developing a suitablepressure-transmitting-fluidfor use inservo-mechanisms and hydraulic;braking systems and the like particularly as they relate to aircraftwhereinspecial problems are encountered. Hydraulic fluids havingaicastor oil base or a polymer-thickened petroleum base have beenemployed in aircraft sys tems for some time but these compositions haveto swell the various parts made of rubber or the like which are used inpressure-transmitting systems. "Various glycols have heretofore beentested for this. purpose but have proven unsatisfactory due to theirextremely high viscosity at the low temperatures (-40 F. and below)which may bezencountered during aircraft operation particularly at highaltitudes. Moreover, the cost of the" glycol-base hydraulic fluidsheretofore proposed has been excessive due to the factthat they cannotbe mixed with Water because glycolwater mixtures do nothave asufficiently low freezing point to remain liquid at these extremely lowtemperatures. v

Various water-base hydraulicfluids have also been proposed but haveprovenunsatisfactory due to their low surface tension which resultsins-"marked" tendency of the fluid to leak out through materials whichwould normally confine a fluid of high surface tension.

Accordingly, one object of the present invention is to provide a new anduseful hydraulic fluid composition 'which will overcome thedisadvantages of the prior art compositions.

the like which is non-inflammable, which is capable of operating at highunit-pressures, which has a sufficiently low freezing point to permitits use in aircraft and which is capable of maintaining appropriateviscosity and lubricity at both low and high operating temperatures. Afurther object is to provide a hydraulic fluid which'will notappreciably corrode, attack or otherwise deleteriously affect thevarious metallic and non-metallic materials commonly employed in servosystems or hydraulic braking systems or the like. 7

Other objects and advantages of the present invention will be apparentfrom the following detailed description and from the appended claims.Generally speaking, the present invention contemplates a new andimproved hydraulic fluid composition prepared by reacting tall oil(which is a commercially available oil composed essentially of mixturesof rosin and resin acids a'n'd'fatty acids obtained as a by-product inthe treatment of wood-pulp in paper mills) with an alkylene oxide (asfor example ethylene oxide or propylene oxide) and thereafterincorporate ing the reaction product into a fluid composition comprisingessentially ethylene glycol and water along with small amounts ofappropriate and well-known corrosion inhibitors, vaporphase inhibitorsand oil-soluble detergents.

In preparing the tall oil-alkylene oxide reaction product referred toabove tall oil is heated to a temperature of about 350 F. to 450 F. in asuitable pressure chamber. Ethylene or propylene oxide under a pressureof about 3000 pounds per square inch is then gradually introduced intothe pressure chamber and the pres sure is allowed to rise in thereaction chamber until it exceeds 2000 pounds per square inch, afterwhich it is maintained during the reaction period within the range fromabout 2000 pounds per square inch to 3000 pounds per square inch. Theamount of alkylene oxide introduced is preferably in the range fromabout 14 moles alkylene oxide per mole of tall oil to about 18 molesalkylene oxide per mole of tall oil. A somewhat improved product may beobtained by a preliminary purification of the tall oil which may becarried out by heating the tall oil with about 1% by weight of maleicacid and then filtering off the precipitated material. Where thispreliminary purification step is employed the amount of alkylene oxideis calculated with respect to the amount of purified tall oil introducedinto the reaction chamber. The final re action product is obtained byallowing the reaction mixture to cool and then adding a few parts byweight of decolorizing charcoal after which the mixture is stirredand'filtered. The final filtrate is heated to about F. and agitated todrive off substantially all unreacted alkylene oxide.

The alkylene oxide-treated tall oil (the exact composition of which isnot known but which appears to be an esterified product) is thenincorporated into a mixture of ethylene glycol or propylene glycol andwater. To the mixture are also added small amounts of one or more in- 3hibitors such as sodium mercaptobenzothiozole, ortho benzoicethanolamine, polymethyl'siloxane, Z-amino, 2-methyl, 1-propanol anddiisopropylamine nitrite.

The following examples represent preferred embodiments of the novelhydraulic fluid compositions of the present invention.

Example I parts by weight of ethylene oxide-treated tall oil is mixedwith 45 parts of ethylene glycol and 35 parts of water. The resultnigfluid is an excellent hydraulic fluid which is non-inflammable, and hasa pour point of minu 70 F. Itskinematic viscosity is approximately 10.5centistokes at 130 F., 450 centistokes at -40 F. and 2350 centistokes atminus 65 F. The fluid has a freezing point of about 85 F. and a boilingI point of about 235 F. The fluid is a true solution at all temperaturesbetween the pour point and the boiling point and remains homogeneousthroughout this temperature range. The fluid has no appreciable tendencyto vaporize at any temperature much below its boiling point so thatthere is no danger of vapor lock resulting at high-temperatureoperation.

As used in the present specification and the appended claims, theexpression alkylene oxidetreated tall oil is intended to mean thereaction products obtained when tall oil is reacted with an alkyleneoxide under conditions of elevated, temperature and elevated pressure.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential attributes thereof, and itistherefore desired that the present embodiments be considered in allrespects as illustrative and not restrictive, reference being had to theappended claims rather than to the foregoing description to indicate thescope of the invention. Having thus described my invention, I claim: 1.A hydraulicfluid composition comprising a mixture consisting essentiallyof about 40-50 parts by weight of a glycol, about 30-40 parts by weightWater, and a minor proportion on the order of about 10-20 parts byweight of the product obtained by reacting an alkylene oxide with talloil at elevated temperature of about 350 F.-450f F. and pressure ofabout 2000-3000 pounds per square inch, said alkylene oxide beingselected from the class which consists of ethylene oxide and propyleneoxide, and being initially present in proportions of about 14-18 molsalkylene oxide per mol tall oil.

2. A hydraulic fluid composition comprising a mixture consistingessentially of about 40-50' parts by weight of a glycol selected fromthegroup which consists of ethylene glycol and propylene glycol, 30-40parts by WBight water, and 10-20 parts by weight of the product ofreaction of about 14-18 mols alkylene oxide with about one mol tall oil,said alkylene oxide being selected from the class which consists ofethylene oxide and propylene oxide, and said reaction being carried outat elevated temperature and pressur 3. A hydraulic fluid compositioncomprising a mixture consisting essentially of about 40-50 parts byweight glycol selected from the group consisting of ethylene glycol andpropylene glycol, -40 parts by weight water, and 10-20 parts by weightof the product of reaction of about 14-18 mols of alkylene oxide withabout one mol tall oil. said alkylene oxide being selected from theclass which consists of ethylene oxide and propylene oxide, and saidreaction being carried out at average temperatures of about 350 F.-450F. and at average pressures of about 2000-3000 pounds per square inch.

4. A hydraulic fluid composition compring' a mixture consistingessentiallyof about 45 parts by weight ethylene glycol, parts by weightwater, and 15 parts by weight of the product of reaction at 350-450 F.and 2000-3000 pounds. per square inch pressure between ethylene oxideand tall oil in a proportion of about 14-18 mols ethylene oxide per moltall oil.

5. A hydraulic fluid composition comprising a mixture consistingessentially of about ;--50 parts by weight ethylene glycol, 30-40 partsby weight water, 1-2 parts by weight light mineral oil, and 10-20 partsby weight of the product of reaction of about 14-18 mols ethylene oxidewith about one mol tall oil, said alkylene oxideFbeing' selected fromthe class which consists of ethylene oxide and propylene oxide, and saidreaction being carried out at average temperatures of about 350 F.-450F. and at average pressures of about 2000-3000 pounds per square inch.

6. A composition as defined in claim 2, further characterized by thefact that the glycol is ethyleno glycol. 'r

7. A composition as defined in claim 2, further characterized by thefact that the glycol is propylene glycol.

8. A composition as defined in claim 2, further characterized by thefact that the alkylene oxide REFERENCES CITED The following referencesare of record in the file of this patent:

V UNITED STATES PATENTS Number Name 1 Date.

2,060,110 Paxton Nov. 10, 19 36 2,457,139 Fife et a1 Dec. 28, 19482,469,493 arker May 10. 1949

1. A HYDRAULIC FLUID COMPOSITION COMPRISING A MIXTURE CONSISTINGESSENTIALLY OF ABOUT 40-50 PARTS BY WEIGHT OF A GLYCOL, ABOUT 30-40PARTS OF WEIGHT WATER, AND A MINOR PROPORTION ON THE ORDER OF ABOUT10-20 PARTS BY WEIGHT OF THE PRODUCT OBTAINED BY REACTING AN ALKYLENEOXIDE WITH TALL OIL AT ELEVATED TEMPERATURE AN ALKYLENE OXIDE WITH TALLOIL AND PRESSURE OF ABOUT 2000-3000 POUNDS PER SQUARE INCH, SAIDALKYLENE OXIDE BEING SELECTED FROM THE CLASS WHICH CONSISTS OF ETHYLENEOXIDE AND PROPYLENE OXIDE, AND BEING INITIALLY PRESENT IN PROPORTIONS OFABOUT 14-18 MOLS ALKYLENE OXIDE PER MOL TALL OIL.